The present invention relates to a method for storing an erasure bit of a CD-ROM (Compact Disc-Read Only Memory), and more particularly to a method for storing the erasure data generated by a compact disc-digital signal processor (DC-DSP) for error correction into a memory.
Generally, the CD-ROM is widely used for a data storage device of a personal computer, and is capable of storing video data, so that it may be used as a memory device for game softwares. Besides the CD-ROM may be employed interactively (CD-I) so as to reduce external memory devices. Moreover, the CD-ROM is systematically compatible with an audio compact disc (CD), and there may be stored into the audio regions computer data, static images, graphic data, musical sounds, vocal sounds, etc. The CD-ROM has a maximum storage capacity of 540 Mega bytes that may allow mass copyings and distributions. The error correction of the CD-ROM is doubly performed both in a conventional CD and the CD-ROM, and therefore the rate of the error correction becomes high so as to give the bit error rate of about 10.sup.-12 bits/(after correction), so that the CD-ROM enables the data processing of high reliability.
The general operation of a CD-ROM system is described with reference to FIG. 1. The data retrieved from a CD by a optical pickup 2 is converted by an RF amplifier 3 into an RF signal processed by an audio signal processor 5. If the RF signal is identified as an audio signal, it is transferred directly to speakers. However, if the RF signal is a data of the CD-ROM such as computer data, static video data, etc., it is transferred through a CD-ROM signal processor 7 to a host computer 8.
Referring to FIG. 2, the CD-ROM signal-processor 7 firstly stores the data generated from the audio signal processor 5 into an external memory 6, and corrects errors, then transferring the error-corrected data to the host computer 8. Conventionally, the external memory 6 comprises two RAMs, RAM1, and RAM2, respectively to store the data and the erasure bit. Namely, the substantial data and the erasure data generated from the audio signal processor 5, after being processed by the CD-ROM signal processor 7, are respectively stored into the first and second RAMs, RAM1 and RAM2, with corresponding addresses. In this case, since the erasure data has one bit per one byte of the substantial data, the second RAM, RAM2, for the erasure data of the external memory 6 is not fully occupied so as to produce vacant regions, so that the working efficiency of the external memory 6 is decreased with the undesirable increase of the PCB's size.